It is known that in silver halide photographic elements, silver ions can be reduced to form metallic deposits of silver. When these deposits are unintended, such as when a camera containing the element leaks light thus exposing the element, or when physical pressure is applied to the element's emulsion layers by, for example, a component of a camera, then they are termed fog. Fog can be formed locally or generally. Described above are two ways in which to form local fog. General fog, which occurs more or less uniformly across an entire element or emulsion layer, is typically formed in response to the ambient conditions in which the element is stored. For example, many high speed photographic elements, such as camera negative films, are susceptible to general fog formation and sensitivity loss when they are stored for an extended period of time in conditions of high temperature and humidity. General fog may also be formed by action of reducing agents contained in the photographic elements, or which are generated during storage thereof.
It has been known that certain palladium salts, when incorporated into a high speed photographic emulsion, stabilize the emulsion and impart to it an increased resistance to fog formation and sensitivity loss. Palladium glycine complexes, in particular, have been known to control general fog formation and sensitivity loss in high speed photographic elements stored under tropical conditions. Accordingly, such palladium complexes are utilized in many photographic silver halide camera negative materials currently commercialized. Palladium compounds have also been proposed for use as scavengers for cyanide which may be generated from components incorporated in a photographic element or its packaging. Uses of palladium complexes are described, e.g., in U.S. Pat. Nos. 2,552,229, 2,566,245, 2,598,079 and 4,892,808; European Patent Applications 0 572 022; 0 578 225; and 0 597 312; Soviet Union Patent 1,656,491; and German Patent 1,157,077. In U.S. Pat. No. 2,552,229, e.g., the sensitivity, gamma, and fog-inhibiting effects of a series of palladium complexes on high speed silver bromoiodide emulsions under varying temperature and humidity storage conditions are explored. In EP 0 572 022, palladium compounds are proposed as cyanide scavengers for hydrogen cyanide gas generated in photographic elements comprising silver halide emulsion layers containing gold and chalcogen sensitized silver halide grains and a thiocyanate salt. EP 0 597 312 describes the use of palladium compounds to protect photographic elements from fog generated by chlorinated s-triazine hardeners and photographically useful chemical compounds containing cyano groups. EP 0 439 069 describes restricting the amount of cyanide generating compounds used in a photographic element in order to control fog generation.
The photographic industry has also long recognized the need to provide photographic films and papers with antistatic protection to prevent the accumulation of static charges during manufacture and use. Such protection is advantageous in photographic elements as static charges can cause irregular fog patterns in photographic silver halide imaging emulsions. Static charges are also undesirable because they attract dirt to the photographic element and this can cause repellency spots, desensitization, fog and physical defects. To prevent the problems arising from an accumulation of static charges, it is a conventional practice to provide an antistatic layer (i.e., a conductive layer) in a photographic element.
Photographic elements further typically comprise some form of antihalation protection. Halation has been a persistent problem with photographic films comprising one or more photosensitive silver halide emulsion layers coated on a transparent support. The emulsion layer diffusely transmits light, which then reflects back into the emulsion layer from the support surface. The silver halide emulsion is thereby reexposed at locations different from the original light path through the emulsion, resulting in "halos" on the film surrounding images of bright objects.
One method proposed for antistatic and antihalation protection in photographic films comprises providing a dyed or pigmented layer behind a clear support as an antihalation backing layer, wherein the backing layer is designed to be removed during processing of the film. Typical examples of such antihalation backing layers comprise a light absorbing dye or pigment (such as carbon black) dispersed in an alkali-soluble polymeric binder (such as cellulose acetate hexahydrophthalate) that renders the layer removable by an alkaline photographic processing solution. Such carbon containing "rem-jet" backing layers have been commonly used for antihalation protection in motion picture films. The carbon particles additionally provide antistatic protection prior to being removed. While such rem-jet backing layers provide effective antihalation and antistatic protection for photographic films prior to processing, their use requires special additional processing steps for their subsequent removal, and incomplete removal of the carbon particles can cause image defects in the resulting print film. Additionally, it is often desirable to provide "process surviving" antistatic protection for photographic elements in order to prevent static build-up even after imagewise exposure and processing, especially for motion picture films which are subject to rapid transport through projection apparatus where static charges can attract dust particles which may detrimentally impact a projected image.
Accordingly, alternatives for carbon-containing, process-removable, antihalation/antistatic backing layers for photographic materials are desirable. One such alternative is to use an antihalation layer or layers containing filter dye or silver metal coated between the support and the emulsion layers, wherein the filter dye or silver is solubilized and removed and/or decolorized during processing of the film, and a separate process-surviving antistatic backing layer. Process-surviving antistatic layers typically include, e.g., ionic polymers, electronic conducting non-ionic polymers, and metal halides or metal oxides in polymeric binders. Conductive fine particles of crystalline metal oxides dispersed with a polymeric binder have been found to be especially desirable for preparing optically transparent, humidity insensitive, antistatic layers for various imaging applications.
Many different metal oxides, such as AnO, TiO.sub.2, ZrO.sub.2, Al.sub.2 O.sub.3, SiO.sub.2, MgO, BaO, MoO.sub.3, and V.sub.2 O.sub.5, are disclosed as useful as antistatic agents in photographic elements or as conductive agents in electrostatographic elements in such patents as U.S. Pat. Nos. 4,203,769, 4,275,103; 4,394,441; 4,416,963; 4,418,141; 4,431,764; 4,495,276; 4,571,361; 4,999,276; and 5,122,445. The use of metal oxide materials is further advantageous, as their antistatic properties allow the use of a protective overcoat layer such as a layer of cellulosic material to provide abrasion protection and/or enhance frictional characteristics while still providing acceptable antistatic performance. Antistatic layers which contain vanadium pentoxide have been found to provide excellent protection against static and are highly advantageous in that they have excellent transparency and their performance is not significantly affected by changes in humidity.
Photographic print elements generally have been found to be far less susceptible to fog generation upon storage under high humidity conditions than camera negative films. Relatively small grain, high chloride emulsions (e.g., emulsions having average grain size equivalent circular diameters of less than about 1 micron and halide contents of greater than 50 mole % chloride) are typically used in photographic print films and papers in order to optimize print image quality and enable rapid processing. Such emulsions typically result in relatively low speed photographic elements in comparison to camera negative films. Low speed is compensated for by the use of relatively high intensity print lamps or lasers for exposing such print elements. For comparison purposes, it is noted that print films and papers, such as motion picture color print films, e.g., when rated using the same international standards criteria used for rating camera negative films, would typically have an ISO speed rating of less than 10, which is several stops slower than the slowest camera negative films in current use.